Peripheral kappa opioid receptor activation drives cold hypersensitivity in mice
Noxious cold sensation is commonly associated with peripheral neuropathies, however, there has been limited progress in understanding the mechanism of cold pain. Here we identify a role for kappa opioid receptors (KOR) in driving noxious cold hypersensitivity. First, we show that systemic activation of KOR by the agonist U50,488 (U50), increases the latency to jump and the number of jumps on a cold plate at 3{degrees}C, and that the KOR antagonist NorBNI attenuates U50-induced noxious cold hypersensitivity. However, the central administration of NorBNI does not block U50-induced noxious cold hypersensitivity, suggesting that peripheral KOR may modulate this effect. To directly test this, we use the peripherally-restricted KOR agonist, ff(nle)r-NH2 and also show selective activation of peripheral KOR causes noxious cold hypersensitivity. To begin to understand how peripheral KOR drive noxious cold hypersensitivity we investigated whether KOR interact with transient receptor potential ankyrin 1(TRPA1) channels, known to facilitate the perception of noxious cold, in dorsal root ganglion (DRG). Using fluorescent in situ hybridization, we show that KOR mRNA colocalizes with the transcripts for the cold-activated TRPA1 channels in DRG. We also show a potentiation in intracellular calcium release in DRG neurons during the simultaneous application of the TRPA1 agonist, mustard oil (MO), and a KOR agonist, U50, when compared to MO alone. Together our data suggest that peripheral KOR may induce noxious cold hypersensitivity through modulation of TRPA1 channels.